The present invention relates to a brake system, and more particularly, to a brake system which allows an increased braking effort to be obtained by a direct intensification of a master cylinder pressure.
In a conventional practice, a brake system for automobiles is provided with a brake booster which boosts an input to an output of a given magnitude through a negative pressure or a hydraulic pressure such as a liquid pressure. The output having an increased magnitude from the booster actuates a master cylinder to generate a master cylinder pressure in an attempt to achieve a braking effort of an increased magnitude with a reduced force of depression applied to a brake pedal.
A brake system provided with a negative pressure booster conventionally utilizes a negative pressure which is generated in an engine. However, with a recent trend toward a reduced fuel cost of an engine, the magnitude of a negative pressure that is generated by the engine tends to be lower, with a consequent reduction in the output from the negative pressure booster. To accommodate for such a reduction in the output, it may be contemplated to increase the size of the negative pressure booster. However, it is impractical to install a negative pressure booster of an increased size in an engine room.
On the other hand, a brake system which is provided with a liquid pressure booster requires the provision of components such as a pump, an accumulator and the like, disadvantageously resulting in an increased overall cost of the system.
It is desirable for a brake system in the event of a quick brake operation to generate a braking effort of an increased magnitude as quickly as possible and more rapidly than for a normal gentle braking operation.
Generating a braking effort of a greater magnitude is another requirement of a quick brake operation. For a beginner driver who is not experienced with driving an automobile, a failure of depressing a brake pedal through an increased stroke may result in a failure to generate a braking effort of a greater magnitude. In these circumstances, it is desirable that an assistance be provided to allow even such a driver to be able to generate a braking effort of a greater magnitude in a reliable manner.
However, such a demand cannot be met with a conventional brake system having a substantially fixed servo ratio for servo control of a braking operation, which prevents a braking effort of a greater magnitude from being generated in a quick brake operation more rapidly than in a normal brake operation, thus precluding the chance of affording any assistance to an unexperienced driver for reliably generating a braking effort of a greater magnitude.
A brake system provided with a conventional booster exhibits a braking effort which remains constant for an equal pedal stroke. However, if the braking effort remains constant for an equal pedal stroke, a flexible accommodation such as improving the brake maneuverability as by improving the operating feeling is precluded.
In view of the forgoing, it is an object of the invention to provide a brake system having a simple construction which enables a braking effort of a greater magnitude to be generated as required through an intensification of a master cylinder pressure while assuring a smooth operation.
It is another object of the invention to provide a brake system which allows the brake effectiveness to be enhanced at the commencement of the intensification.
It is a further object of the invention to provide a brake system which allows a pedal stroke to be reduced during the time the intensification is activated.
According to a first aspect of the invention, there is provided a brake system including a reservoir of braking liquid, a master cylinder defined in a housing to develop a master cylinder pressure therein as an associated master cylinder piston advances through the master cylinder, and a wheel cylinder which is fed with the master cylinder pressure, and comprising intensifying means for causing the master cylinder piston to advance as required to intensify the master cylinder pressure, the intensifying means comprising an intensifying chamber defined rearward of the master cylinder piston within the housing, a source of pressure connected to the intensifying chamber, an input shaft having a front portion disposed close to the intensifying chamber and mechanically coupled to a brake operating member to cause the master cylinder piston to advance, and a control valve mechanism disposed between the front end of the input shaft and the rear end of the master cylinder piston for switching a communication between the intensifying chamber and the reservoir, the control valve mechanism comprising a bottomed guide opening formed in at least one of the rear end of the master cylinder piston and the front end face of the input shaft, and a spool valve slidably fitted into the guide opening and having one end which abuts against at least one of the rear end of the master cylinder piston and the front end of the input shaft, whereby a radial misalignment between the axes of the master cylinder piston and the input shaft is tolerated.
According to a second aspect of the invention, there is provided a brake system including a reservoir of braking liquid, a master cylinder defined in a housing to develop a master cylinder pressure therein as an associated master cylinder piston advances through the master cylinder and a wheel cylinder which is fed with the master cylinder pressure, and comprising intensifying means for causing the master cylinder piston to advance as required to intensify the master cylinder pressure, the intensifying means comprising an intensifying chamber defined rearward of the master cylinder piston within the housing, a source of pressure connected to the intensifying chamber, an input shaft having a front portion disposed close to the intensifying chamber and mechanically coupled to a brake operating member to cause the master cylinder piston to advance, and a control valve mechanism disposed between the front end of the input shaft and the rear end of the master cylinder piston for switching a communication between the intensifying chamber and the reservoir, the control valve mechanism being movable relative to the master cylinder piston, further comprising stroke reducing means for controlling the relative positions of the control valve mechanism and the master cylinder piston such that the stroke of the input shaft is reduced as compared with the stroke of the master cylinder piston.
According to a third aspect of the invention, there is provided a brake system including a reservoir of braking liquid, a master cylinder defined in a housing to develop a master cylinder pressure therein as an associated master cylinder piston advances through the master cylinder, and a wheel cylinder which is fed with the master cylinder pressure, and comprising intensifying means for causing the master cylinder piston to advance as required to intensify the master cylinder pressure, the intensifying means comprising an intensifying chamber defined rearward of the master cylinder piston within the housing, a source of pressure connected to the intensifying chamber, an input shaft having a front portion disposed close to the intensifying chamber and mechanically coupled to a brake operating member to cause the master cylinder piston to advance, and a control valve mechanism disposed between the front end of the input shaft and the rear end of the master cylinder piston for switching a communication between the intensifying chamber and the reservoir, the input shaft comprising a reaction piston having a front end disposed close to the intensifying chamber, and an input plunger slidably fitted inside the inner periphery of the reaction piston and having a rear end which is connected to the brake operating member, the reaction piston and the input plunger having engageable portions which engage each other when the reaction piston retracts through a given distance relative to the input plunger, further comprising a resilient member disposed between the reaction piston and the master cylinder piston for urging the reaction piston forwardly.
In accordance with the first aspect of the invention, the provision of the intensifying means permits the master cylinder pressure to be intensified as required to provide a braking effort of an increased magnitude. In addition, a radial misalignment of the axes of the master cylinder piston and the input shaft is tolerated, permitting a smooth operation.
In accordance with the second aspect of the invention, the provision of the intensifying means which intensifies the master cylinder pressure and the stroke reducing means which reduces the stroke of the input shaft as compared with the stroke of the master cylinder piston allows the master cylinder pressure to be intensified as required to provide braking effort of an increased magnitude while permitting the stroke of the input shaft to be reduced as compared with the stroke of the master cylinder piston when the master cylinder pressure is intensified by the intensifying means.
In accordance with the third aspect of the invention, the provision of the intensifying means allows the master cylinder pressure to be intensified as required to provide a braking effort of an increased magnitude with a simple construction. In addition, since the input shaft is constructed with the reaction piston and the input plunger so that the transmission of a reaction from the pressure in the intensifying chamber to the input shaft is variable, when it is desired to intensify the master cylinder pressure by the intensifying means, a gradient in the pressure intensification at the commencement of the intensifying action can be made higher, allowing the brake to be more effective at the commencement of the intensifying action.
Above and other objects, features and advantages of the invention will become apparent from the following description of several embodiments thereof with reference to the attached drawings.